The present invention relates to a pipe connection for use in a ventilating duct system having ducts with circular cross-section.
In ventilating duct systems, use is made of different pipe connections for connecting and branching the system. Such pipe connections are often called xe2x80x9cpipe fittingsxe2x80x9d by those skilled in the art. Pipe fittings of this type are shown, for instance, in the catalogue xe2x80x9cVentilationxe2x80x9492xe2x80x9d issued by Lindab AB in 1992. Moreover, pipe fittings are described in an SIS document called SS-EN 1506 and issued in November 1998, entitled (in English) xe2x80x9cVentilation for buildingsxe2x80x94Sheet metal air ducts and fittings with circular cross-sectionxe2x80x94Dimensionsxe2x80x9d.
In a method of joining a pipe fitting with a ventilating pipe, the end portion of the fitting is inserted into the pipe, a sealing ring mounted at the end of the fitting ensuring the seal of the pipe joint. This is illustrated on the page xe2x80x9cSafe 5xe2x80x9d in the above-mentioned Lindab catalogue. Similar pipe fittings with a sealing ring are shown in the FIG. A.1(d) and FIG. A.3(c) in the above-mentioned SIS document.
Further examples of pipe connections of this type are described in CH-A-646,233 and in U.S. Pat. No. 4,050,703 and WO 94/15133. A common feature of these prior-art pipe connections is that the sealing ring is arranged in a circumferential groove adjacent to the end of the pipe fitting. U.S. Pat. No. 3,955,834 also belongs to prior art and discloses similar pipe connections and sealing constructions, including embodiments in which the sealing ring is clamped in the end of the pipe fitting by the terminal edge thereof being bent radially outwards/backwards.
The nominal diameter of ventilating ducts and pipe fittings of this type is according to standard between 63 mm and 1,250 mm (see Table 1 in the SIS document). As a rule, the sealing ring of the pipe fittings is placed close to the end of the fitting independently of the nominal diameter. This causes certain mounting problems especially for diameters exceeding 630 mm, as will be explained in more detail below.
When a pipe fitting having a greater diameter is to be connected to a ventilating pipe, the fitting is slightly inclined when being inserted into the pipe. In technical language, the fitting is made to enter. During such entering, first an outer circumferential portion of the end of the fitting is placed on an inner circumferential portion of the outer tube at the end thereof. Then the fitting is turned to a position coaxially with the pipe and is finally inserted into the same.
In connection with greater diameters, the ventilating pipes made of thin sheet metal are somewhat oval at the end, which means that the entering operation will be complicated. It is in fact difficult to insert the inclined pipe fitting to such an extent that the entering can be carried out. The pipe ends quite simply do not fit together. Since the distance between the end of the pipe fitting and the groove in which the sealing ring is arranged is comparatively small, the so-called entering edge of the fitting is too small to be able to efficiently remodel the oval shape of the outer pipe. By entering edge is here meant the distance between the end of the pipe fitting and the groove where the sealing ring is arranged. In prior-art pipe fittings with a folded terminal edge, the axial length of the entering edge usually constitutes about 1% of the diameter of the fitting.
Another drawback that arises during entering is that the circumferential portion of the pipe fitting which is first placed on the inside of the outer pipe easily xe2x80x9cjumps out ofxe2x80x9d the pipe when the fitting is to be turned in place for insertion.
A further inconvenience is that the lips of the sealing ring are easily folded in the wrong direction in the final part of the entering operation, which may cause insufficient sealing action and undesirable pressure drop in the duct, which in turn causes noise and increased energy costs.
An object of the present invention is to obviate the above drawbacks and provide a pipe connection which is improved relative to prior art.
According to the invention, this and other objects that will appear from the following specification are now achieved by a pipe connection for use in a ventilating duct system having ducts with circular cross-section, the pipe connection being adapted to be partially and with a close fit inserted into and connected with an outer pipe, the pipe connection having a circumferential groove, in which a circumferential seal is arranged, which in an inserted position of the pipe connection abuts and seals against an inside of the outer pipe, the pipe connection having a terminal edge portion which is adapted to be inserted into the outer pipe and which comprises an outer conical portion with a diameter decreasing towards an end of the pipe connection. The terminal edge portion of the pipe connection further comprises a circumferential guide surface which has such a diameter that the close fit is obtained and which is located between the groove and the conical outer portion, and the terminal edge portion has an axial length which constitutes about 1.5-5.5% of the diameter of the guide surface.
By the terminal edge portion of the pipe connection, i.e. the portion between the end of the pipe connection and the groove in which the sealing ring is arranged (the entering edge), being formed with a greater axial extent than in prior-art pipe connections, the inventive pipe connection will have a longer end portion which during entering is inserted into the outer pipe. As a result, the pipe connection can be inserted more easily also into somewhat oval outer pipes, and the pipe connection is kept in the pipe during the turning that takes place during entering. Since the sealing ring is arranged axially further inwards on the pipe connection, it will be positioned outside the outer pipe during the entire entering operation, which means that there is no risk of its sealing lips being folded in the wrong direction towards the inside of the outer tube. The risk of pressure drop and leakage in the pipe joint is thus reduced.
Altogether this means that the inventive pipe connection is more mounting-friendly than prior art pipe connections. In particular, the mounting staff need not use such mounting aids as have up to now been necessary owing to the oval shape of the larger ventilating pipes.
The entering of the pipe connection is facilitated by its outer conical portion which has a diameter decreasing towards the end of the pipe connection. Certain degrees of conicity have been found particularly advantageous. In a preferred embodiment, the conical portion has at its end a diameter which is about 97-99.9% of the diameter of the guide surface, preferably about 98%.
The combination of the suggested axial length of the terminal edge portion (1.5-5.5% of the diameter of the guide surface) and the above-mentioned conditions for conicity, i.e. the diameter of the conical portion at the end of the pipe connection, results in a very advantageous embodiment which means a considerably improved mounting.
The terminal edge portion or entering edge of the pipe connection comprises the outer conical portion and the neighboring guide surface which is arranged axially inwardly thereof. The axial length ratio of these two portions of the entering edge preferably has a certain distribution. The entering operation is most effective if the conical portion constitutes about 40-70% of the total axial length of the entering edge. Most preferred the range is 50-65%, and in particular the value 55% is advantageous.
According to an additional preferred embodiment, the pipe connection has a further guide surface positioned axially inside the groove in which the sealing ring is arranged. This additional guide surface preferably has the same diameter as the guide surface of the entering edge. As a result, the pipe joint will be more stable and straight compared with prior-art technique, which is due to the fact that the outer pipe rests with a close fit against two guide surfaces on each side of the groove.